1. Field of the Invention
This invention relates to an articulated vehicle comprising a trailing unit which is pivotally supported at the front by a leading unit.
2. Description of the Prior Art
The trailing unit, part of whose weight is carried by the leading unit, is usually referred to as the semi-trailer and may in turn be connected to a full trailer, i.e. a trailer having front and rear axles. In the normal situation in which the leading unit houses the engine and is the only driving unit, it is referred to as the tractor. However, it will be appreciated that there may be circumstances in which it is preferable for the engine to be carried by the trailing unit.
The articulated highway truck is recognized as the most economical vehicle for the movement of goods on paved highways. For on/off highway use rigid frame vehicles are considered essential at present, owing to the higher percentage of gross weight imposed on the drive axles which in turn provides better traction to overcome the combination of high rolling resistance coupled with lower wheel adhesion factors.
Thus the vehicle which is the most economical (owing to its high legal and practicable payload) is precluded from a very substantial sector of the commercial and military vehicle market because of its inherently low tractive capability on poor surfaces. It is known that articulated vehicles are being marketed with hydrostatic drive to the trailer axles but these have a low performance due to the difficulty of matching the speeds of the direct mechanically driven front axles to those of the hydrostatically driven trailer axles.
It would therefore be desirable to be able to provide a method of driving the axle or axles of an articulated truck's semi-trailer at the same speed as the drive axle or axles of the tractor regardless of steering lock angle between the tractor and semi-trailer.
A problem with articulated vehicles is that, during turning, the trailing unit cuts in on the leading unit, i.e. the inside turning radius is considerably smaller than the outside turning radius, so that a large amount of space is needed to maneuver the vehicle. This problem becomes worse if a full trailer is attached to a semi-trailer. It would therefore also be desirable to prevent cutting-in by the trailing unit.